This current clamp can be used to detect a current of up to 30A. Simply clip it around the current source that you wish to measure and it will produce a (very) small AC voltage proportional to the current. The cable is terminated on one end with a standard 3.5mm jack (like a headphone jack).

Use this to build your own energy monitor and keep your power usage down, or use it to to build an >over-current protection device for an AC load. See the link below for an example project. Check out the datasheet for the pinout of the 3.5mm jack